Foreign object detection in wireless charging systems and related apparatuses and methods

1. An apparatus, comprising:

an analog-to-digital converter to sample at least one of a coil voltage potential and a coil current representation of a transmit coil inductively coupled to a receive coil of a wireless power receiver with a distance between the transmit coil and the receive coil; and

a processing core to determine an expected reference Q-factor value responsive to the at least one of the sampled coil voltage potential and the sampled coil current representation, the expected reference Q-factor value indicating a Q-factor value expected at a predetermined reference wireless power transmitter inductively coupled to the wireless power receiver with a reference distance from a reference transmit coil of the predetermined reference wireless power transmitter to the receive coil of the wireless power receiver, a transmitter coil type of the predetermined reference wireless power transmitter different from a transmitter coil type of the wireless power transmitter, the determination of the expected reference Q-factor value taking into consideration any difference between the distance and the reference distance.

2. The apparatus of claim 1 , wherein the processing core is to determine that a foreign object is detected responsive to a determination that the expected reference Q-factor value is less than a reference Q-factor value received from the wireless power receiver.

3. The apparatus of claim 1 , wherein the processing core is to determine that a foreign object is detected responsive to a determination that the expected reference Q-factor value is less than a product of a tolerance factor and a reference Q-factor value received from the wireless power receiver.

4. The apparatus of claim 3 , wherein the tolerance factor is 0.9.

5. The apparatus of claim 1 , wherein the processing core is to determine that a foreign object is detected responsive to a determination that the expected reference Q-factor value is less than a reference Q-factor value received from the wireless power receiver minus a threshold value.

6. The apparatus of claim 1 ,

wherein the analog-to-digital converter to sample at least one of the coil voltage potential and the coil current representation of the transmit coil without being inductively coupled to the receive coil of the wireless power receiver,

wherein the processing core is to determine a transmitter only inductance value and a transmitter only resistance value of a tank circuit of the wireless power transmitter.

7. The apparatus of claim 6 , wherein the processing core is to determine a combined transmitter-receiver inductance and a combined resistance of the tank circuit with the receive coil in proximity to the transmit coil responsive to the at least one of the coil voltage potential and the coil current representation.

8. The apparatus of claim 7 , wherein the processing core is to determine:

a reflected inductance by subtracting transmitter only inductance from the combined transmitter-receiver inductance; and

a reflected resistance by subtracting transmitter only resistance from the combined resistance.

9. The apparatus of claim 8 , wherein the processing core is to determine a multiplication factor to be a square root of a ratio between a product of a reference inductance of a reference tank circuit of the predetermined reference wireless power transmitter and the reference distance and a product between the transmitter only inductance and the distance.

10. The apparatus of claim 9 , wherein the processing core is to determine the expected reference Q-factor value to be a function of a ratio between a first quantity and a second quantity, the first quantity including the reference inductance plus a product between the multiplication factor and the reflected inductance, the second quantity including a reference resistance of the reference tank circuit plus a product between the multiplication factor and the reflected resistance.

11. A method of operating a wireless power transmitter, the method comprising:

sampling at least one of a coil voltage potential and a coil current representation of a transmit coil inductively coupled to a receive coil of a wireless power receiver with a distance between the transmit coil and the receive coil; and

determining an expected reference Q-factor value responsive to the at least one of the sampled coil voltage potential and the sampled coil current representation, the expected reference Q-factor value indicating a Q-factor value expected at a predetermined reference wireless power transmitter inductively coupled to the wireless power receiver with a reference distance from a reference transmit coil of the predetermined reference wireless power transmitter to the receive coil of the wireless power receiver, a transmitter coil type of the predetermined reference wireless power transmitter different from a transmitter coil type of the wireless power transmitter, the determination of the expected reference Q-factor value taking into consideration any difference between the distance and the reference distance.

12. The method of claim 11 , comprising determining that a foreign object is detected responsive to a determination that the expected reference Q-factor value is less than a reference Q-factor value received from the wireless power receiver.

13. The method of claim 11 , comprising determining that a foreign object is detected responsive to a determination that the expected reference Q-factor value is less than a product of a tolerance factor and a reference Q-factor value received from the wireless power receiver.

14. The method of claim 13 , wherein the tolerance factor is 0.9.

15. The method of claim 11 , comprising determining that a foreign object is detected responsive to a determination that the expected reference Q-factor value is less than a reference Q-factor value received from the wireless power receiver minus a threshold value.

16. The method of claim 11 , comprising:

sampling at least one of the coil voltage potential and the coil current representation of the transmit coil without the transmit coil being inductively coupled to the receive coil of the wireless power receiver; and

determining a transmitter only inductance value and a transmitter only resistance value of a tank circuit of the wireless power transmitter.

17. The method of claim 16 , comprising determining a combined transmitter-receiver inductance and a combined resistance of the tank circuit with the receive coil in proximity to the transmit coil responsive to the at least one of the coil voltage potential and the coil current representation.

18. The method of claim 17 , comprising determining:

a reflected inductance by subtracting transmitter only inductance from the combined transmitter-receiver inductance; and

a reflected resistance by subtracting transmitter only resistance from the combined resistance.

19. The method of claim 18 , comprising determining a multiplication factor to be a square root of a ratio between a product of a reference inductance of a reference tank circuit of the predetermined reference wireless power transmitter and the reference distance and a product between the transmitter only inductance and the distance.

20. The method of claim 19 , comprising determining the expected reference Q-factor value to be a function of a ratio between a first quantity and a second quantity, the first quantity including the reference inductance plus a product between the multiplication factor and the reflected inductance, the second quantity including a reference resistance of the reference tank circuit plus a product between the multiplication factor and the reflected resistance.